Self aligning non contact shadow ring process kit

ABSTRACT

The invention provides a removable first edge ring configured for pin and recess/slot coupling with a second edge ring disposed on the substrate support. In one embodiment, a first edge ring includes a plurality of pins, and a second edge ring includes one or more alignment recesses and one or more alignment slots for mating engagement with the pins. Each of the alignment recesses and alignment slots are at least as wide as the corresponding pins, and each of the alignment slots extends in the radial direction a length that is sufficient to compensate for the difference in thermal expansion between the first edge ring and the second edge ring.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of co-pending U.S. patentapplication Ser. No. 09/459,313, filed Dec. 10, 1999. Each of theaforementioned related patent applications is herein incorporated byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an improved susceptor whichinhibits the deposition of process gasses on the edge and backside of asubstrate, and which may be easily removed and cleaned.

[0004] 2. Description of the Related Art

[0005] Chemical vapor deposition (CVD) is one of a number of processesused to deposit thin films of material on semiconductor substrates. Toprocess substrates using CVD, a vacuum chamber is provided with asusceptor configured to receive a substrate. In a typical CVD chamber,the substrate is placed into and removed from the chamber by a robotblade and is supported by a substrate support during processing. Aprecursor gas is charged into the vacuum chamber through a gas manifoldplate situated above the substrate, where the substrate is heated toprocess temperatures, generally in the range of about 250° to 650° C.The precursor gas reacts on the heated substrate surface to deposit athin layer thereon and to form volatile byproduct gases, which arepumped away through the chamber exhaust system.

[0006] A primary goal of substrate processing is to obtain the largestuseful surface area, and as a result the greatest number of chips,possible from each substrate. This is highlighted by the recent demandsfrom semiconductor chip manufacturers to minimize edge exclusion on thesubstrates processed, so that as little of the substrate surface aspossible, including the edge of the wafer, is wasted. Some importantfactors to consider include processing variables that affect theuniformity and thickness of the layer deposited on the substrate, andcontaminants that may attach to the substrate and render all or aportion of the substrate defective or useless. Both of these factorsshould be controlled to maximize the useful surface area for eachsubstrate processed.

[0007] One source of particle contamination in the chamber is materialdeposited at the edge or on the backside of the substrate that flakesoff or peels off during a subsequent process. Substrate edges aretypically beveled, making deposition difficult to control over thesesurfaces. Thus, deposition at substrate edges is typically nonuniformand, where metal is deposited, tends to adhere differently to adielectric than to silicon. If a wafer's dielectric layer does notextend to the bevel, metal may be deposited on a silicon bevel andeventually chip or flake, generating unwanted particles in the chamber.Additionally, chemical mechanical polishing is often used to smooth thesurface of a substrate coated with tungsten or other metals. The act ofpolishing may cause any deposits on the edge and backside surfaces toflake and generate unwanted particles.

[0008] A number of approaches have been employed to control thedeposition on the edge of the substrate during processing. One approachemploys a shadow ring which essentially masks a portion of the perimeterof the substrate from the process gasses. One disadvantage with theshadow ring approach is that, by masking a portion of the substrate'sperimeter, the shadow ring reduces the overall useful surface area ofthe substrate. This problem is made worse if the shadow ring is notaccurately aligned with the substrate, and alignment can be difficult toachieve.

[0009] Another approach employs a purge ring near the edge of thesubstrate for delivering a purge gas along the substrate's edge toprevent edge deposition. The purge gas limits or prevents the depositiongas from reaching the substrate and thus limits or prevents depositionon the wafer's beveled edge. A third approach uses a shutter ring and apurge ring in combination to form a purge gas chamber having a purge gasinlet and outlet adjacent the substrate's edge so as to guide the purgegas across the wafer's edge.

[0010] A wafer typically sits inside (radially) the purge ring, with agap therebetween. Conventionally, purge rings are made of aluminum andare welded to the substrate support in an effort to prevent the ringfrom deforming during processing. However, during the thermal cyclingwhich occurs within a CVD processing chamber, the aluminum ringsnonetheless deform, losing the integrity of their shape and thereforecompromise their ability to keep particles from depositing on thesubstrate's edge. This can change the size of the gap, leading tonon-uniformity of deposition across the wafer's edge. As the aluminumrings expand and contract, material thereon can flake, and createparticles which can contaminate the wafer.

[0011] Further, in order for the rings to work effectively for shadowingand/or for purging, they must be frequently cleaned to remove depositionmaterial which can alter the gap or flake off and contaminate the wafer.Such cleaning increases chamber downtime, reduces throughput and resultsin higher operating costs.

[0012] Accordingly a need exists for an improved susceptor which canreliably prevent edge deposition, and which can be easily cleaned.

SUMMARY OF THE INVENTION

[0013] In one aspect, the present invention overcomes the problems ofthe prior art by providing a substrate support having a removable edgering, which may be made of a material having a lower coefficient ofthermal expansion (CTE) than that of the substrate support. The edgering may be a shadow ring, a purge ring, or function as both edge ringand shadow ring. The edge ring and the substrate support are configuredfor pin and slot coupling. In one aspect, either the edge ring or thesubstrate support includes a plurality of pins, and the other of theedge ring or the substrate support includes a plurality of alignmentslots in which the pins may be inserted. Each of the slots is at leastas wide as a corresponding one of the plurality of pins and extends inthe radial direction. a length that is sufficient to compensate for thedifference in thermal expansion between the substrate support and theedge ring.

[0014] In another aspect, the invention provides a removable first edgering positioned above the substrate support and configured for pin andslot coupling with a second edge ring attached to the substrate support.Preferably, either the first edge ring or the second edge ring includesa plurality of pins, and the other of the first edge ring or second edgering includes one or more alignment recesses and one or more alignmentslots. The pins are inserted into the alignment recesses and alignmentslots to couple the two edge rings in alignment. Each of the alignmentrecesses and alignment slots are at least as wide as the correspondingone of the plurality of pins, and each of the alignment slots extends inthe radial direction a length that is sufficient to compensate for thedifference in thermal expansion between the first edge ring and thesecond edge ring.

[0015] Other objects, features and advantages of the present inventionwill become more fully apparent from the following detailed descriptionof the preferred embodiments, the appended claims and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] So that the manner in which the above recited features of thepresent invention can be understood in detail, a more particulardescription of the invention, briefly summarized above, may be had byreference to embodiments, some of which are illustrated in the appendeddrawings. It is to be noted, however, that the appended drawingsillustrate only typical embodiments of this invention and are thereforenot to be considered limiting of its scope, for the invention may admitto other equally effective embodiments.

[0017]FIG. 1 is an exploded perspective view of a susceptor of theinvention;

[0018]FIG. 2 is a side view, in pertinent part, of a susceptor of theinvention;

[0019]FIG. 3 is a side view, in pertinent part, of a susceptor of theinvention;

[0020]FIG. 4 is a side view in pertinent part of a susceptor of theinvention;

[0021]FIGS. 5A and 5B are side views in pertinent part of a susceptor ofthe invention;

[0022]FIG. 6 is a side view in pertinent part of a susceptor of theinvention;

[0023]FIG. 7 is a side view of a chamber showing a susceptor of theinvention in a non-processing position.

[0024]FIG. 8 is a top view of a shadow ring of the invention;

[0025]FIG. 9 is a top view of a shadow ring supported on a chamber bodyring of the invention;

[0026]FIG. 10 is a side view of a chamber showing a susceptor of theinvention in a processing position; and

[0027]FIG. 11 is a side view of a chamber showing a susceptor of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028]FIG. 1 is an exploded perspective view of a susceptor 11 a. Thesusceptor 11 a comprises a substrate support 13, adapted for pin andslot coupling with an edge ring, such as purge ring 15. Specifically,the substrate support 13 comprises three pins 19 a-c which extendupwardly from the top surface of substrate support 13. The bottomsurface of the purge ring 15 comprises three alignment slots 17 a-cpositioned to interface with the three pins 19 a-c. The substratesupport 13 comprises a central wafer supporting surface 13 a, and thethree pins 19 a-c are disposed substantially equally spaced around thesubstrate supporting surface 13 a. Each of the slots 17 a-c is at leastas wide as the corresponding pin 19 a-c, and extends radially outwardfrom the center of the substrate supporting surface 13 a, in thedirection in which the substrate support 13 expands and contracts duringthermal cycling.

[0029] The substrate support 13 is preferably made of a metal such asaluminum, as is conventional. The purge ring 15 is generally made of amaterial having a lower coefficient of thermal expansion (CTE) than theCTE of the substrate support 13 material. Preferably the purge ring 15is made of a ceramic material. The slots 17 a-c extend a length which issufficient to compensate for the difference in thermal expansion betweenthe substrate support 13 and the purge ring 15, over the range ofprocess temperatures to which the susceptor 11 a is exposed. Thisdifference in thermal expansion may be due to the different CTE of thepurge ring 15 material and the substrate support 13 material. Preferablyeach pin 19 a-c is surrounded by a pad 21 made of a thermally insulatingmaterial, so as to achieve thermal insulation between the substratesupport 13 and the purge ring 15, as further described below withreference to FIG. 2. The pads 21 are preferably made of a highlypolished ceramic and therefore allow the purge ring 15 to slide easilytherealong while minimizing particle generation. The purge ring 15 mayfurther include a plurality of wafer guide pins 23 to facilitateaccurate wafer placement, as is disclosed in U.S. patent applicationSer. No. 09/103,462 filed Jun. 24, 1998 (incorporated herein in itsentirety).

[0030]FIG. 2 is a side view, in pertinent part, of a susceptor 11 a,having a wafer W positioned thereon. As shown in FIG. 2 the substratesupport 13, the purge ring 15 and the slots 17 a-c are configured suchthat with use of the pad 21, no direct contact exists between thesubstrate support 13 and the purge ring 15. By thermally insulating thepurge ring 15 from the metal substrate support 13, the purge ring 15experiences less thermal stress then would otherwise result if the purgering 15 were to directly contact the typically higher temperaturesubstrate support 13. Also as shown in FIG. 2, the slot 17 a has a depthgreater than the length of the pin 19 a to reduce thermal conductionfrom the substrate support 13 to the purge ring 15, via the pin 19 a.

[0031] The slots 17 a-c extend radially outward relative to the centerof the substrate support 13 and preferably are each just slightly widerthan the respective pin 19 a-c. This prevents the purge ring 15 movementlaterally relative to the substrate support occuring as a result ofthermal cycling induced expansion and contraction from being more thanthe maximum distance allowing clearance between the slot 17 a and thepin 19 a pair. The pins 19 a-c also restrict rotational movement of thepurge ring 15 relative to the substrate support 13, thereby providingrotational alignment.

[0032] The substrate support 13 comprises a purge gas delivery channel25 and a diffuser ring 13 b which couples purge gas from the purge gasdelivery channel 25 through a purge gas distribution channel 27 definedby an inner edge of the diffuser ring 13 b and an outer edge of thesubstrate support 13, and then through a plurality of small orifices Oformed in the diffuser ring 13 b to a lower edge of the purge ring 15.

[0033] In operation the wafer W is positioned on the wafer supportingsurface 13 a such that the edge of the wafer W is positioned adjacentthe outlet of the purge slot 29. In this manner as purge gas flowsupwardly through the purge slot 29 along the edge of the wafer W,deposition on the wafer's edge is prevented. During a depositionprocess, the susceptor 11 a is typically heated to a temperature in therange of 350° to 475° C., typically by a heating coil embedded in orcontacted with the underside of, the susceptor 11 a. However, forchamber maintenance or cleaning, the susceptor 11 a is typically allowedto cool back to ambient temperatures.

[0034] This temperature change causes thermal expansion and contractionof the chamber elements, including the substrate support 13 and thepurge ring 15. Despite thermal cycling which occurs during CVDprocessing, and the resulting expansion and contraction of the substratesupport 13 and the diffuser ring 13 b, thermally induced stresses arenot imposed upon the purge ring 15, as it (and the pins 19 a-csupporting it) can move radially as the temperature changes, due to thepin 19 a-c and slot 17 a-c coupling. Any thermally induced expansion ofthe gap between the purge ring 15 and the wafer W is insignificant.Accordingly edge deposition is more uniformly and reliably prevented.Moreover, the purge ring 15 may be easily lifted off the pins 19 a-c forroutine cleaning or replacement. Accordingly downtime is minimized.

[0035]FIG. 3 is a side view, in pertinent part, of a susceptor 11 b. Theinventive susceptor 11 b of FIG. 3 is similar to the susceptor 11 a ofFIG. 2, except the substrate support 13 of FIG. 2 does not comprise thediffuser ring 13 b. Instead, the purge gas delivery channel 25 deliverspurge gas to a purge gas distribution channel 27 which is defined by aninner edge of the purge ring 15 and an outer edge of the substratesupport 13, as is the more narrowly defined purge gas slot 29. Theembodiment of FIG. 3 requires fewer parts, and replaces the orifices O(of FIG. 1) with a restrictor gap R. The restrictor gap R is formed by ahorizontal notch in the substrate support 13 and a correspondinghorizontal protrusion in the purge ring 15. The size of the restrictorgap R is determined by the respective vertical dimensions of thesubstrate support 13 and the purge ring 15 to the horizontal notch orprotrusion, and by the thickness of the pad 21. The embodiment of FIG. 3reduces clogging because the restrictor gap R which expands radiallyaround the substrate support 13 in a continuum is less likely to clogthan are the plurality of orifices. By reducing the number of parts, theFIG. 3 embodiment also reduces the probability of differential expansiontherebetween and the resultant particle generation. Note that, like theFIGS. 1 and 2 embodiment, the purge ring 15 rests on the insulator pads21 and is aligned by the pins 19.

[0036]FIG. 4 is a side view, in pertinent part, of a susceptor 11 c. Asshown in FIG. 4, the purge ring 15 of the inventive susceptor 11 c has aplurality of pins 19 (only one shown) which extend downward from thebottom surface of the purge ring 15. The pins 19 are pressed into thepurge ring 15 and the pads 21 are secured to the pins 19 in the samemanner, or maybe integral to the pins 19. In operation, each pin 19 isinserted within a corresponding slot 17 located on the substrate support13. In this example the slots 17 are formed in the diffuser ring portion13 b of the substrate support 13. Thus, FIG. 4 shows that the positionsof the pins 19 and the slots 17 may be switched, and still achieve theadvantages of pin and slot coupling.

[0037]FIGS. 5A and 5B are side views, in pertinent part, of a susceptor11 d. The purge ring 15 a of FIGS. 5A and 5B is configured such that theinner edge 15 a overhangs the edge of the wafer W. Thus, the purge ring15 a functions as both a purge ring 15 a and a shadow ring 4(overhanging or shadowing the wafer's edge). The pin and slot couplingof FIGS. 5A and 5B allows the substrate support 13 to expand andcontract without affecting the shape or position of the purge ring 15 a,as described above with reference to FIGS. 2 and 3. FIG. 5A shows thepurge ring 15 a in a process position, and FIG. 5B shows the purge ring15 a in a wafer W transfer position. Because shadow rings 4 overlap thewafer's edge, they are conventionally supported in a wafer W transferposition above the substrate support 13 (e.g., by a hanger or lip whichprotrudes from the chamber wall) while a wafer W is placed on orextracted from the substrate support 13. After a wafer W is placed onthe substrate support 13, the substrate support 13 elevates and engagesthe bottom of the shadow ring 4, transferring the shadow ring 4 from thelip to the substrate support 13 as further described below.

[0038] Conventional substrate supports 13, whether to be used with apurge ring 15 and/or shadow ring 4, are initially lowered to a wafer Wtransfer position. A wafer handler then carries a wafer W into positionabove the substrate support 13 and the lift pins (not shown) lift thewafer W off the wafer handler. Thereafter, the wafer handler retracts,and the substrate support 13 is further elevated to engage the shadowring 4.

[0039]FIG. 6 is a side view in pertinent part of a susceptor 11 e. Theinventive susceptor 11 e is configured to facilitate access to the purgegas distribution channel 25 for cleaning. Specifically, the surface ofthe substrate support 13 in which the pin 19 (or in an alternativeembodiment, the slot 17) is located, is below the outlet of the purgegas distribution channel 25. Thus, when the purge ring 15 and/or shadowring 4 is removed from the substrate support 13, the gas distributionchannel's outlet is exposed. To further facilitate cleaning, the purgegas distribution channel 25 may be angled upwardly (preferably between0° and 30° ), as shown in FIG. 6.

[0040]FIG. 7 is a side view of a chamber showing a susceptor 11 f of theinvention in a lowered non-processing position. The susceptor 11 fcomprises a removable first edge ring, such as a shadow ring 4,supported by a chamber body ring 200 disposed on the internal surface102 of the processing chamber body 100 above the substrate support 13and a second ring, such as a purge ring 15, disposed on the substratesupport 13. The purge ring 15 may be attached to the substrate support13 as described above relating to FIGS. 1-6. The substrate support maybe made of various materials, such as aluminum and ceramic, and mayinclude a heating element, such as a resistive heating coil. The shadowring 4 comprises a plurality of tapered or frustoconically shaped pins19 (two shown), equally spaced around the perimeter of the shadow ring 4and extending downwardly therefrom. The purge ring 15 includes at leastone tapered or frustoconically shaped alignment recess 5 and at leastone tapered or frustoconically shaped alignment slot 6 formed therein.Although the invention is shown and described with a shadow ring havingpins thereon and a purge ring having recess/slot thereon, it isunderstood that invention contemplates embodiments wherein the pin andrecess/slot coupling may be disposed on either the shadow ring or thepurge ring. The invention also contemplates embodiments wherein eitherthe pins or the recesses/slots include tapered surfaces.

[0041] The pins 19 are positioned to interface with the alignment recess5 and the alignment slot 6. The alignment recess 5 and the alignmentslot 6 are at least as wide as a corresponding one of the plurality ofpins 19. In one aspect, the width is defined as the dimensionperpendicular to the radial direction, relative to the center of thepurge ring 15. Referring to FIG. 8, which is a top view of a purge ring15 of the invention showing the alignment recess 5 and the alignmentslot 6, line 800 represents the radial direction relative to the centerof the purge ring 15, and line 802 represents the directionperpendicular to the radial direction relative to the center of thepurge ring 15. The width of the alignment slot 6, being the dimensionperpendicular to the radial direction relative to the center of thepurge ring 15, is shown by segment 804. The radial dimension of thealignment slot 6 is shown by segment 806. The alignment slot 6 extendsin a radial direction, relative to the center of the purge ring 15, alength that is sufficient to compensate for any difference in thermalexpansion between the purge ring 15 and the shadow ring 4. The radialdimension (i.e., length) of the alignment slot 6 is up to about sixtymils greater, preferably up to about forty mils greater, than the radialdimension of the corresponding pin 19. The width of the alignment recess5 and alignment slot 6 is between about three mils and about ten milswider, preferably between about three mils and about eight mils wider,than the width of the corresponding pin 19. The coupling of the pins 19with the alignment recess 5 and the alignment slot 6 restricts movementof the shadow ring 4 caused by thermal cycling induced expansion andcontraction or other causes to less than the length of the alignmentslot 6. The pins 19 also restrict rotational movement of the shadow ring4 relative to the purge ring 15, thereby providing rotational alignment.

[0042] The pins 19 as shown in FIG. 7 preferably have a frustoconicalshape, tapering from a base portion to a top portion. The alignmentrecess 5 and the alignment slot 6 have matching tapering sidewallsforming a wider opening portion and a narrower bottom portion forreceiving the tapered pins 19. This configuration allows for andcorrects gross misalignment between the two rings because the narrowertip portion of the pins 19 can be inserted into the wider openingportion of the recess 5 and slot 6 with a greater margin ofmisalignment. Thus, with frustroconically shaped or tapered pins 19instead of non-tapering (i.e., cylindrical) pins, recess 5, and slot 6,misalignment of the shadow ring 4 with the purge ring 15, due to thermalexpansion or other causes can be corrected when the pins 19 are insertedinto the recess 5 and slot 6 when the rings come together. As the pins19 are inserted into the recess 5 and slot 6, misalignment between theshadow ring and the purge ring is corrected as the surface of the pin 19slides along the surface defined by the recess 5 or slot 6. The tworings are aligned as the pins 19 are fully inserted into the recess 5and slot 6.

[0043] The pin 19 and recess 5/slot 6 coupling allows the shadow ring 4to move with respect to the purge ring 15 due to different thermalexpansions between the two rings without imposing stresses on eitherring that could cause ring deformation, flaking or breakage of any ofthe components. The shadow ring 4 remains in pivotal alignment to thepurge ring 15 at the location of the pin 19 and recess 5 coupling, whilethe pin 19 and slot 6 coupling allows the shadow ring to move slightly(i.e., restricted by the length of the slot 6) relative to each otherdue to different thermal expansions between the two rings. The inventionprovides consistent alignment of the shadow ring 4 with the purge ring15 and the substrate. Moreover, the shadow ring 4 may be easily removedfor cleaning or replacement. Down time is thereby minimized.

[0044]FIG. 9 is a top view of a shadow ring 4 supported on a chamberbody ring 200. A chamber body ring 200 is secured to the internalsurface 102 of the chamber body 100. The chamber body ring 200 includesa plurality of recesses 202 formed in the upper portion of the internalsurface 220 of the chamber body ring 200. The shadow ring 4 includes aplurality of projections 10 configured to rest on the surface of thechamber body ring 200 defined by the recesses 202. Preferably, fourprojections 10 are spaced equally along the perimeter of the shadow ring4. When not coupled to the purge ring 15, the shadow ring 4 may besupported by the chamber body ring 200 via the projections 10 resting onthe surface of the recesses 202. The recesses 202 are sized to allow forthermal expansion of the shadow ring 4, and yet keep the shadow ring 4sufficiently aligned with the purge ring 15 so that the pins 19 staywithin the capture range of the recess 5 and slot 6. The sidewallsurfaces of the recess 202 may also be tapered to urge a shadow ring 4into the desired aligned position on the chamber body ring 200.

[0045]FIG. 10 is a side view of a chamber showing a susceptor 11 f in aprocessing position. As shown, the purge ring 15 attached to thesubstrate support 13 contacts and lifts the shadow ring 4. The pins 19of the shadow ring 4 are inserted into the recess 5 and slot 6 of thepurge ring 15. The shadow ring 4 is thereby lifted off the chamber bodyring 200, so that the projections 10 of the shadow ring 4 are lifted offthe internal surface 220 of the chamber body ring 200 defined by therecesses 202. In this configuration, the shadow ring 4 is positionedabout 3 to 5 millimeters above a wafer W and overhangs a portion of theperimeter, or edge, of the wafer W, preventing deposition thereon duringCVD processing.

[0046] In operation, the substrate support 13 is initially lowered to awafer transfer position, as shown in FIG. 7. A wafer handler comprisinga robot blade then carries a wafer into position above the substratesupport 13. Lift pins (not shown) lift the wafer W off the robot blade,and the robot blade retracts. The substrate support 13 is elevated toposition the substrate thereon, and then the substrate support 13further elevates so that the purge ring 15 attached thereto lifts theshadow ring 4 off the chamber body ring 200, as shown in FIG. 10. As thepurge ring 15 engages the shadow ring 4, the pins 19 are inserted intothe alignment recess 5 and alignment slot 6. The tapered surfaces of thepins 19 slides along the tapered surfaces of the alignment recess 5 andalignment slot 6, urging the shadow ring 4 into desired alignment withthe purge ring 15.

[0047]FIG. 11 is a side view of a chamber showing a susceptor 11 g in anon-processing configuration. In this aspect of the invention, thesubstrate support 13 includes a ceramic susceptor and a ceramic purgering 15 disposed thereon. The purge ring 15 and the shadow ring 4include the pin and slot/recess coupling of the invention as describedabove.

[0048] As is apparent from the above description, a chamber such as thechamber described in commonly assigned U.S. patent application Ser. No.09/103,462, filed Jun. 24, 1998 (incorporated in its entirety), whenemploying the inventive susceptor of FIGS. 1 through 5, providessuperior edge deposition prevention and increased throughput as comparedto conventional deposition chambers (CVD, PVD, etc.).

[0049] The foregoing description discloses only the preferredembodiments of the invention, modifications of the above disclosedapparatus and method which fall within the scope of the invention willbe readily apparent to those of ordinary skill in the art. For instance,the inventive susceptor comprises pin and slot coupling between any typeof edge ring (purge ring and/or shadow ring), whether the pins arelocated on the substrate support or the ring. Although each of thefigures shows the use of thermally insulating pads these pads areoptional. Further, it will be understood that a heating element may beincluded in the susceptor, as is conventionally known. Also asconventionally known, each of the purge gas delivery channels 25 of thevarious embodiments of the invention preferably open into a purge gasdistribution channel 27 which also extends somewhat below the opening ofthe purge gas delivery channel 25 (as shown in each of the figures), soas to create a buffer channel which ensures more even distribution ofthe purge gas to the purge slots 29.

[0050] The terms pin and slot are to be broadly interpreted to includeshapes other than straight pins and slots 6 (e.g., rectangular keys,etc.). Further, purge ring or purge ring/shadow ring can beadvantageously removably coupled to a substrate support, by mechanismsother than pin and slot coupling. Any removably coupled purge ring willbenefit from the exposed outlet of the purge gas delivery channel andthe upwardly angled purge gas delivery channel. Similarly a susceptorwhether or not having a removably coupled purge ring, can benefit fromthe definition of a purge gas distribution channel having a restrictorgap between the substrate support and the purge ring. Thus, theseaspects of the invention should not be respectively limited to pin andslot coupling or to removably coupled purge rings.

[0051] While the present invention has been disclosed in connection withthe preferred embodiments thereof, it should be understood that otherembodiments may fall within the spirit and scope of the invention, asdefined by the following claims.

1. An apparatus comprising: a) a substrate support; b) a first edge ringdisposed on the substrate support, the first edge ring having one ormore tapered recesses; and c) a second edge ring having one or morematching tapered pins for mating engagement with the one or more taperedrecesses of the first edge ring.
 2. The apparatus of claim 1 wherein thefirst edge ring includes one or more slots disposed for matingengagement with the one or more tapered pins on the second edge ring. 3.The apparatus of claim 1 wherein the first edge ring comprises a purgering.
 4. The apparatus of claim 1 wherein the second edge ring comprisesa shadow ring.
 5. The apparatus of claim 1 wherein the first edge ringincludes one tapered recess and one diametrically positioned taperedslot, and wherein the second edge ring includes two tapered pinsdiametrically positioned for mating engagement with the recess and theslot.
 6. The apparatus of claim 1 wherein the substrate supportcomprises a purge gas channel, and the first edge ring comprises a purgering.
 7. An apparatus for processing substrates, comprising: a) achamber; b) a substrate support disposed in the chamber; c) a first edgering disposed on the substrate support, the first edge ring having oneor more tapered recesses; and d) a second edge ring having one or morematching tapered pins for mating engagement with the one or more taperedrecesses of the first edge ring.
 8. The apparatus of claim 7, furthercomprising: e) a chamber body ring disposed on an interior surface ofthe chamber, the chamber body ring having one or more recesses forsupporting engagement with the second edge ring.
 9. The apparatus ofclaim 8 wherein the first edge ring includes one or more slots disposedfor mating engagement with the one or more tapered pins on the secondedge ring.
 10. The apparatus of claim 8 wherein the first edge ringcomprises a purge ring.
 11. The apparatus of claim 8 wherein the secondedge ring comprises a shadow ring.
 12. The apparatus of claim 8 whereinthe first edge ring includes one tapered recess and one diametricallypositioned tapered slot, and wherein the second edge ring includes twotapered pins diametrically positioned for mating engagement with therecess and the slot.
 13. The apparatus of claim 8 wherein the substratesupport comprises a purge gas channel, and the first edge ring comprisesa purge ring.
 14. The apparatus of claim 8 wherein the one or morerecesses on the chamber body ring include tapered side surfaces.
 15. Amethod for supporting a substrate in a chamber, comprising: a)positioning the substrate on a substrate support having a first edgering disposed around a substrate supporting surface, the first edge ringhaving one or more recesses; and b) positioning a second edge ring abovethe first edge ring, wherein the second edge ring include one or morepins for mating engagement with the one or more recesses on the firstedge ring.
 16. The method of claim 15 wherein the first edge ringincludes one or more slots disposed for mating engagement with the oneor more tapered pins on the second edge ring.
 17. The method of claim 15wherein the first edge ring comprises a purge ring.
 18. The method ofclaim 15 wherein the second edge ring comprises a shadow ring.
 19. Themethod of claim 15 wherein the first edge ring includes one taperedrecess and one diametrically positioned tapered slot, and wherein thesecond edge ring includes two tapered pins diametrically positioned formating engagement with the recess and the slot.
 20. The method of claim15, further comprising: c) flowing a purge gas around the substrateduring substrate processing.